Telephone switching network



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Si Qu lrmmww 1 3 w23 l .l l l l a l l l .QQ m23 Feb. l5, 1966 H. H. ABBOTT TELEPHONE SWITCHING NETWORK /Nl/ENTOR y H. H. ABBOTT Feb. l5, 1966 H. H. ABBOTT TELEPHONE SWITCHING NETWORK 6 Sheets-Sheet 3 Filed Aug. 5l, 1962 QNOI m. .GFK

/Nl/E/VTOR By h'. H. ABBOTT Q www ATTORNEY Feb. 15, 1966 H, H. ABBOTT 3,235,668

TELEPHONE SWITCHING NETWORK Filed Aug. 3l, 1962 6 Sheets-Sheet 4 /A/l/ENTOR H. H. ABBOTT MQ/lw/d ATTORNEY Feb. l5, 1966 H. H. ABBOTT TELEPHONE SWITCHING NETWORK 6 Sheets-Sheet 5 Filed Aug. 3l, 1962 /Nl/ENTOR By H. h'. ABBOTT Q UMM ATTORNEY Feb. l5, 1966 H. H. ABBOTT TELEPHONE SWITCHING NETWORK 6 Sheets-Sheet 6 Filed Aug 31, 1962 mw S E@ um@ N .SQ

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/NVENTOR B H. H. ABBOTT y@ @M5/4J ATTORNEY United States Patent Ctlce 3,235,668 TELEPHONE SWITCHING NETWORK Henry H. Abbott, Middletown, NJ., assignor to Bell Telephone Laboratories, Incorporated, New York, N.Y., a corporation of New York Filed Aug. 31, 1962, Ser. No. 220,832 19 Claims. (Cl. 179-18) This invention relates in general to communication switching networks and, more particularly, to the electronic control of an electromechanical crosspoint switching network.

There are a variety of known end marked crosspoint switching networks such as gas tube networks of the type described in Patent 2,684,405 of July 20, 1954, to E. Bruce and H. M. Straube and such as electronic crosspoint switching networks employing PNPN crosspoint devices. In both the gas tube networks and the PNPN networks busy paths are excluded from subsequent selection by means of electrical lockout circuits whose operation depends upon the negative impedance characteristics of the crosspoint devices.

Switching networks are known wherein ferreed switches are employed. Ferreed switches generally comprise reed relays together with hysteretic magnetic material whereby closure of the relay contacts may be controlled by ux paths determined by the remanent state or states of the magnetic material. Such devices have been described in a number of places in the literature including A. Feiner et al. Patent 2,995,637, issued August 8, 1961, and an article The Ferreed--A New Switching Device, by A. Feiner, C. A. Lovell, T. N. Lowry, and P. G. Ridinger, Bell System Technical Journal, volume 39, No. 1, January 1960, page 1. As used herein the terms ferreed switch or ferreed is intended to apply to devices of the types therein described.

Further such networks are known wherein the ferreed switches are employed in a plurality of stages to provide selective interconnection between lines and between lines andtrunks in a telephone switching system. For example, in T. N. Lowry Patent 3,037,085, May 29, 1962, there is disclosed a ferreed circuit arrangement for a switching network in which theferreeds are connected for dilerentialexcitation, as further described in the Lowry patent, the above-mentioned publication, and additionally discussed below. In application Serial No. 206,055, tiled June 28, 1962, now W. S. Hayward, Jr., Patent 3,110,772 issued November 12, 1963, there is disclosed a common bus circuit for interconnecting the control conductors of a matrix of ferreed switches, and in T. N. Lowry application Serial No. 205,920, led June 28, 1962, there is disclosed a crosspoint switching network employing a plurality of stages of ferreed switches and means for controlling the establishment and disestablishment of paths through such a network.

In the aforenoted Lowry application Serial No. 205,920, a record of the availability of the links of the switching network is maintained in an external memory map. Such a memory map vmay Ibe yadvantageously employed in a large switching system; however, the routines for finding an available path through interrogation of the memory map are relatively complex and where, as in a small PBX or community dial oilice, a relatively small number of lines and trunks are to be served by a switching network, the use lof a memory map andits attendant access circuitry may be impractical.

The ferreed is an electromechanical `devi-ce which is particularly suitable for use as a crosspoint device in-an electronically controlled switching network. The ferreed is responsive to current pulses of extremely short time duration; of the vorder generated by electronic -control circuitry. However, in that a ferreed device does not ex- 3,235,668 Patented Feb. 15, 1966 hibit negative impedance characteristics, the use of lockout arrangements in the control of a ferreed network is not possible. It is for this reason that ferreed networks in the past have been associated with-a link memory map and attendant access circuitry.

It is a general object of this invention to substantially reduce the common memory, selection, and control circuitry requirements for electronically controlled switching networks.

It is a further object of the invention to eliminate the requirement of a memory map circuit which is separate and distinct from electronically controlled switching networks.

It is another object of the invention to eliminate the requirement of external network access control and logic circuitry in electronically controlled switching networks.

These and other objects of this invention are attained in one specific illustrative embodiment wherein a switching network is arranged in a plurality of switching stages, each stage of which comprises a plurality of ferreed crosspoint arrays. VEa-ch of the ferreed crosspoint arrays is similar to the ferreed crosspoint array described in the aforementioned W. S. Hayward, Jr., Patent 3,110,772. The Hayward disclosure is incorporated herein by reference and, although a brief functional description of the ferreed crosspoint array disclosed in the Hayward application is included hereinbelow, further details thereof may be ascertained by reference to the Hayward application.

In one specific structural arrangement of a ferreed switch, as further described in A. L. Blaha et al` application Serial No. 124,723, tiled July 17, 1961, Patent 3,075,059 issued January 22, 1963, one or more dry reed contacts are surrounded by a thin sleeve of square loop magnetic material. A magnetic shunt plate positioned at the midpoint of the sleeve separates the sleeve magnetically into two independent halves. When the two halves are magnetized series-aiding, the flux return path is through the reeds, causing them to close. When the two halves `are magnetized in series opposition, the flux through the reeds is a minimum, causing the reeds to open. Each end of the sleeve has two windings, one winding having a larger number of turns than the other. The winding with the larger number of turns on one end of the sleeve is connected in series opposition with the winding having the fewer number of turns on the other end of the sleeve. When either of the sets of windings thus formed is energized, the two ends of the sleeve are poled oppositely and the contacts are opened. When the two sets of windings are energized simultaneously with equal currents, the two sleeve ends are poled series-aiding and the contacts are closed.

The basic ferreedcrosspoint is arranged in coordinate array to form 8 x 8 switches. Two sets of reed contacts are used to connect tip and ring conductors from one stage of the network to the next. A third set of reed contacts is used to connect a signaling conductor from one stage of the network to the next. The control windings, two per ferreed, are series-connected along the rows and columns of an array. Internal to the array, lone end of the control windings of rows and columns forms a com-mon multiple. To close a crosspoint, current is passed in one column and out one row via the common multiple. The lcrosspoint at the intersection of the row and column closes. At the same time, current passes through one of the two windings of all other ferreeds in the same row and column causing any that are operated to release. This dierential method of operation is characterized by the absence of specific crosspoint release operations.

Crosspoints are released as a direct result of other crosspoints being closed, and at the same time as the other -crosspoints are closed, in accordance with the principles lof differential excitation of ferreeds, as referred to above.

Each of the equipments between which connections are established through the switching network has associated therewith a control conductor for applying marking potentials and crosspoint control signals to the network, a signaling conductor for applying link control potentials to the network and transmission conductors for communication purposes. The switching stages of the network are connected by links each of which comprises a control conductor for extending applied marking potentials and crosspoint enabling signals through the network, a signaling conductor for extending applied link control potentials through the network and transmission conductors for providing a communications path through the network. Each ferreed crosspoint device includes contacts for interconnecting signaling conductors and contacts for interconnecting transmission conductors.

The cathodes and anode elements of a three-terminal PNPN device are included in series with the control conductor of eachlink. The gate element of the PNPN device is connected to the signaling conductor of the link. When a link is idle, the associated PNPN device is connected so as to assume its conductive state in response to marking potentials applied to its anode and cathode. When a link is busy and not available for inclusion in another path, a link control potential applied to the signaling conductor of the busy link inhibits the associated PNPN device from assuming its conductive state. In its nonconductive state, the PNPN device excludes both marking potentials and crosspoint enabling signals from the control lead of the link, thereby precluding the selection or release of the busy link.

Selection of available links for establishing a path through the switching network is accomplished by squentially scanning the possible paths between the equipments to be connected until an idle path is found. A crosspoint enabling signal is then applied to the control lead associated with one of the equipments to be connected. The appropriate crosspoint devices are operated in response to the crosspoint enabling signal, and the communication path between equipments is thereby established.

In accordance with a feature of the invention, the busy or idle condition of a path through a switching network is indicated by the electrical continuity of the control leads of the links of which the path is comprised.

In accordance with another feature of the invention, link selection in the switching network is accomplished by sequentially determining the electrical continuity of the control leads which define the possible paths between a marked input terminal and a marked output terminal.

In accordance with a further feature of the invention, links are selectively excluded from selection in accordance with the potential applied to the signaling conductors thereof.

In accordance with another feature of the invention, links are selectively excluded from release in accordance with the potential applied to the signaling conductors thereof.

In accordance with still another feature of the invention, the control lead of each link includes a unidirectional current device in circuit therewith, which is selectively inhibited from assuming a conductive condition in accordance with the potential applied to the signaling conductor of the link.

In accordance with a still further feature of the invention, the control conductor of each link is electrically isolated from the control conductors of all other links by the aforenoted unidirectional current device, thereby precluding false operation of crosspoint devices over control conductors other than the control conductor of a selected link.

These and other objects and features of this invention will be more readily understood from the following description when read with respect to the drawing, in which:

FIGS. 1, 2, and 3 are a general block diagram of a l switching network in accordance with the broad aspects of this invention;

FIGS. 4, 5 and 6 are a schematic representation of one illustrative embodiment of this invention;

FIG. 7 is a schematic representation of portions of the control circuity used in selecting and establishing a path through the switching network;

FIG. 8 is a schematic representation of one embodiment of a ferreed crosspoint device;

FIG. 9 shows the arrangements of FIGS. l, 2 and 3; and

FIG. 10 shows the arrangement of FIGS. 4, 5, and 6.

GENERAL DESCRIPTION FIGS. l, 2, and 3 show the general arrangement of one specific illustrative embodiment of the invention. Lines L0-L191 and trunks Ffil-T63 illustrate equipments between which connections may be established through the switching network. The network is arranged in three switching stages; the first or primary stage (FIG. l) comprising eight primary crosspoint arrays PAO-PA7, each having twenty-four inputs and eight outputs; the secondary stage (FIG. 2) comprising eight secondary crosspoint arrays SAO-SA7, each having eight inputs and eight outputs; and the third or tertiary stage (FIG. 3) comprising eight tertiary crosspoint arrays TAO-TA7, each having eight inputs and eight outputs.

The primary and secondary switching stages are connected by sixty-four primary links PLO-PL63, which connect the eight outputs of each primary crosspoint array PAO-PA7 to inputs of each secondary crosspoint array SAO-SA'7. The primary links PLO-PL63 are so arranged that each primary array PAO-PA7 has one primary link PLO-PL63 connecting it to each secondary array SA()- SA7.

The secondary and tertiary switching stages are connected by sixty-four secondary links, SUI-SL63, which connect the eight outputs of each secondary array SAO- SA7 to inputs of each tertiary array TAO-TA7. The secondary links, SLO-SL63, are arranged similarly to the arrangement of primary links PLO-PL63 in that each secondary array SAO-SA7 has one secondary link SLO- SL63 connecting it to each tertiary array TAO-TA7.

The primary arrays, PAO-PA7, and the tertiary arrays, TAO-TA?, may advantageously be similar to the crosspoint array described in the aforementioned copending patent application Serial No. 206,055 of W. S. Hayward, Ir., now Patent 3,110,772.

Each of the lines L0-L191 (FIG. l) has associated therewith a control conductor such as LOC, a signaling conductor such as L08 yand transmission conductors such as LOT and LOR. Similarly, each of the trunks rfil-T63: (FIG. 3) has associated therewith a control conductor such as TOC, a signaling conductor such as TS and transmission conductors such as TOT and TOR.

Each primary link PLO-PL63 (FIG. 1) is comprised of a control conductor such as PLOC, a signaling conductor such as PLOS, transmission conductors such as PLOT and PLOR and a link control circuit such as PLCO.

Each of the secondary links SLO-SL63 (FIG. 2) is comprised of a control conductor such as SLOC, a signaling conductor such as SL08, transmission conductors such as SLUT and SLOR, and a link control circuit such as SLCO.

The secondary arrays SAO-SA7, are also similar to the aforementioned ferreed crosspoint array of the Hayward` application. However, in departure from the Hayward disclosure, a link selection circuit, such as LSO, is included in series with the common bus SAtlB-SA'B of each secondary array SAO-SA7.

Line selector circuit 201 comprises means for selectively applying a marking potential to any of the control. conductors LOC-L191C, each of which is associated with one of the lines L0-L191. Trunk selector 301 is similar to line selector 201 and comprises means for selectively extending marking potentials and crosspoint enabling signals from link selector control 302 to any of the control conductors TOC-T63C, each of which is associated with one ofthe trunks Til-T63. Line selector 201 and trunk selector 301 form no part of the inventive concept of this invention and are therefore not described in detail herein.

Link selection A brief description will now be given of the establishment of a transmission connection through the network. Aline, such las line L0, is selected by line selector circuit 201 and a marking ground potential is applied thereby to the control conductor LOC associated with line LO. A trunk, such as trunk TO, is selected by trunk selector circuit 301 and a positive battery marking potential is applied to the control conductor TOC associated with the selected trunk TO; The positive battery marking potential is applied through the link selection control circuit 302, conductor LSCl, and the trunk selector circuit 301 to the control conductor TOC.

Tertiary array TAO, which serves trunk TO, is connectable to each of the secondary arrays SAO-SA7 through secondary links SLO-SL17, respectively. Primary array PAO, which serves line LO, is connectable to each of the secondary arrays SAOSA7 through primary links PLO- PL7, respectively. There are,` therefore, eight possible paths through which trunkTO and line L0 may be connected. Each of these paths is unique to one of the secondary arrays SAO-SA7.

It is to be noted at this point that, although the specific illustrative embodiment of-the invention being described .comprises a particular network-arrangement of links and crosspoint arrays, the only criteria of the network arrangement of this invention are that one intermediate switching stage of a plurality of switching stages comprises a plurality of crosspoint arrays each of which is unique to one of the possible paths for connecting each input terminal to each output terminal of the network, and that the number of possible paths-between an input terminal and an output terminal is equal to the number of crosspoint arrays in that intermediate switching stage.

It is assumed, for this example, that all of the eight possible paths between line LO and trunkvTO` `are idle. The link selectioncircuits LSO-LS7 sequentially examine th'e paths unique to their associatedv secondary array, SAO-SA7, respectively. The busy or idle condition of each path is determined by ascertaining whether or not the path is electrically continuous. The rst path examined in which current ilow is'produced responsive to the marking potentials` applied to control conductors TOC and LOC is selected for use. Upon locating an idle path, the link selection circuit associated with the secondary array to which the located idle path is unique signals link selector control 302 over conductor LSCZ, and the scanning of possible paths is halted. Link selector control 302 signals pulse source 303 to apply a crosspoint enabling signal over conductor F01, through link selector control 302, conductor LSCl, and trunk selector circuit 301, to controlconductor TOC. The crosspoint enabling signal is passed through tertiary array TAO and over the eight control conductors SLOC-SL7C of secondary links SLOLT Assuming that the path unique to secondary array SAO has been selected, link selection circuit LSO completes the circuit of the common bus SAOB of secondary array SAO, thereby permitting the crosspoint enabling signal to pass through secondary array SAO. The common buses SA1B-SA7B ofsecondary arrays SA1-SA7 remain open. The crosspoint enabling signal generated by pulse source 204 is therefore precluded from passing` through secondary arrays SA1-SA7.

The crosspoint enabling signal, which was permitted to pass through secondaryl array SAO, continues through the control conductor PLOC of primary link PLO, primary array PAO, control conductor LOC of line L0 and the line selector circuit 201 to thepreviously applied marking ground potential. The crosspoint devices in primary array PAO, secondary array SAO and tertiary array TAO which define this selected path are operated in response to the crosspoint enabling signal. Signaling conductors LOS, PLOS, SLOS, and TOS are interconnected by contacts associated with the enabled crosspoint devices. Transmission conductorsLOT and LOR, PLOT and PLOR, SLOT and SLOR, and TOT and TOR are also respectively interconnected by contacts associated with the operated crosspoint devices.

The signaling yconductors TOS-T638 are connected to busy-idle switches TSO-TS63, respectively, in'trunks TO through T63. Busy-idle switches TSO-TS63 are operated responsive to a busy condition of the trunk TO-T63 associated therewith, which operation may be performed either manually Iby an operator or automatically by wellknown supervisory switching circuitry. When operated, busy-idle switches TSO-T563 selectively apply a link control potential from link control potential source 304 to signaling conductors TOS-T63S, respectively.

It is assumed that busy-idle switch TSO vin trunk TO has been operated, either manually `or automatically, and that a link control potential has been applied to signaling conductor TOS. This potential is extended through the network -over signaling conductors SLOS and PLOS.

Secondary link control circuits SLCOSLC63 are responsive to a link control potential applied to their associated signaling conductors SLOSLGSS, respectively, to inhibit current flow in the associated control conductors SLOC-SL63@ respectively. Primary link control circuits PLCO-PLC63 are responsive to the application of link control potential to their associated signaling conductors PLOS-PL63S, respectively, to inhibit current flow through the associated control conductor-s PLOC-PL63C, respectively.

Primary link control circuit PLCO` and secondary link control circuit SLCO are therefore responsive to the link control potential applied by busy-idle switch TSO to signaling conductor TOS to inhibit current flow in control conductors PLOC and SLOC, respectively, thereby excluding marking potentials and crosspoint enabling signals from the selected path. Since the selecting operations performed by the network are dependent upon the electrical continuity of a path through the network, the selection of primary link PLO and secondary link SLO for inclusion in subsequent connections is prevented until busyidle switch TSO isreturned to the idle position and the link control potential is removed from the signaling conductors TOS, SLOS, and PLOS. When a connection has been established between a selected line and a selected trunk, the marking potentials applied by line selector 201 and trunk selector 301 are removed.

As previously described, the ferreed crosspoint devices of the array which dene a selected path between an input terminal and an output terminal of the array are enabled responsive to the application of a crosspoint enabling signal to the output terminal when a marking potential of opposite polarity is appliedl to the input terterminal. path is available from the output terminal through the columnV and row winding sets of the ferreed crosspoint via the common bus, and coincident current will flow through both sets of windings, thereby enabling the ferreed. As further described above, when current ilow exists in only lone winding set of a ferreed crosspoint, the ux path will cause the contacts ofthe ferreed to open. Therefore, when marking ground potential is applied to an input terminal other than the input terminal to which a connection was established, the enabled ferreed will be returned to its disabled state in response to the application of a crosspoint enabling signal tothe original output terminal.

The above-described exclusion of crosspoint enabling signals from the control conductors BLOC and SLOC prelIn this condition, an electrically continuous` 7 vents the disablement of the associated enabled crosspoint devices in tertiary array TAG, secondary array SAG and primary array PAG. The connection between trunk T and line L0 is therefore precluded from release until current fiow in control conductors PLGC and SLOC ceases to be inhibited by link control circuits PLCG and SLCG,

When the transmission conductors of an established connection are no longer required for use, the busy-idle switch TSO-TS63 of the associated trunk T0-T63 is returned to its idle position either manually or 4by wellknown automatic supervisory switching means.

The return of busy-idle switch TSO to its idle position removes link control potential from the signaling conductors TGS, LGS, and PLGS of the connection between trunk T0 and line L0. Responsive to the removal of link control potential from signaling conductors TLGS and SLGS, primary and secondary link control circuits TLCO and SLCG no longer inhibit current flow through control conductors TLGC and SLOC. Marking potentials and crosspoint enabling signals are therefore permitted to pass over control conductors PLOC and SLOC after link control potential has been removed from signaling conductors TLGS and SLOS. Primary link PLO and secondary link SLG are now available for use in establishing subsequent connections through the network.

The contacts associated with the ferreed crosspoint devices which define the now idle connection between line L0 and trunk T0 remain closed. However, the neXt crosspoint enabling signal applied to either the column or row of ferreed devices in the now idle path will return the enabled crosspoints to their disabled states due to the aforementioned differential operation of the ferreed devices.

DETAILED DESCRIPTION The ,ferreed FIG. 8 shows one embodiment of a ferreed crosspoint device which may be advantageously used with this invention and which is as shown in the above-mentioned Blaha et al. disclosure.

Reed contacts 801, 802, and 803 are surrounded by a magnetic sleeve 800. Shunt plate 804 separates the sleeve 800 into two independent halves a and b. Windings 805 and 806 surround the upper half a of sleeve 800; winding'806 having a larger number of turns than winding 805. Windings 807 and 808 surround the lower half b of sleeve 80G; winding 807 having a larger number of turns that winding 808. Windings 805 and 807 are connected in series opposition as are windings 806 and 808.

As previously described, when either terminal 811 or terminal 812 is individually energized, the reed contacts 801, 802, and 803 are opened since the two independent halves a and b of sleeve 80G are poled oppositely. However, when terminals 811 and 812 are simultaneously and equally energized, the two halves a and b of sleeve 800 are poled series-aiding, and contacts 801, 802, and 803 will be closed.

The network FIGS. 4, 5, and 6 of the drawing show in more detail primary array P'A0, secondary arrays SAG and SA7 and tertiary array TAO. Each ferreed crosspoint device, such as crosspoint 401 (FIG. 4) comprises a differentially wound ferreed having three sets of contacts, such as 402, 403, and 404, associated therewith. As described above, ferreed 401 is operable in response to current flow in control conductor PLGC coincident with current flow in control conductor LGC. The contacts 402, 403, and 404 which are controlled by ferreed 401 serve to connect signaling conductor LGS to signaling conductor PLGS and transmission conductors LGT and LGR to transmission conductors PLOT and PLOR, respectively. Primary array PAG (FIG. 4) comprises one hundred ninety-two ferreed crosspoint devices arranged in coordinate array so that each device defines a connection between one `of the lines L0L23 and one of the primary links PLCG-PLCT Cil Tertiary array TAO (FIG. 6) comprises sixty-four ferreed crosspoints arranged in coordinate array so that each crosspoint defines a connection between one of the trunks T0-T'7 and one of the secondary links SLO-SL7. Ferreed 601 .of tertiary array TAG will become enabled in response to current iiow in control conductor TGC coincident with current fioW in control conductor SLGC. The contacts 602, 603, and 604 which are controlled by ferreed 601, -serve to connect signaling conductor TGS to signaling conductor SLGS and transmission conductors TGT and TOR to transmission conductors SLGT and SLGR, respectively, when ferreed 601 yis enabled.

Secondary array SAG (FIG. 5) comprises sixty-four ferreed crosspoints each having three sets of contacts associated therewith. Crosspoint 501 will become enabled in response to current flow in control conductor SLGC coincident with current fiow in control conductor PLGC. The contacts 502, 503, and 504, which are controlled by ferreed S01, serve to connect signaling conductor SLGS to signaling conductor PLGS and transmission conductors SLOT and SLGR to transmission conductors PLOT and PLOR respectively, when crosspoint 501 is enabled.

Primary link PLO includes a primary link control circuit PLCG (FIG. 4). The function of primary link control circuit PLCO is to provide an effective open circuit in control conductor PLOC when the transmission conductors PLOT and PLGR of primary link PLO are in use. Primary link control circuit PLCO comprises a three terminal device PTG, which may advantageously be a silicon controlled rectifier device, having its anode and cathode connected in series with control conductor PLGC and its gate terminal connected to signaling conductor PLGS. When positive battery marking potential is applied to control conductor PLOC, it is extended through resistor PRG to signaling conductor PLGS. This positive battery marking potential applied to the anode and gate elements of rectiiier PTG causes rectifier PTG to assume its conductive or closed circuit state in response to the application of marking ground potential to its cathode, thereby producing current flow in control conductor PLOC, When a link control ground potential is applied to signaling conductor PLGS, rectifier PTG is inhibited from becoming conductive due to the ground potential applied to the gate terminal thereof. A more detailed description of the operating characteristics of a silicon controlled rectifier is contained in the second edition of Silicon `Controlled Rectifier Manual as published by the General -Electric Company in 1961. When rectifier PTO is thus inhibited from becoming conductive, an effective open circuit is produced in control conductor PLGC and no current will fiow therein.

Each of the other primary links PL1-PL7 includes a primary link control circuit, PLC1-PLC7 respectively, similar to primary link control circuit PLCO.

Each secondary link SLO-SL7, includes a secondary link control circuit, SLCO-S'LC7 respectively. The secondary link control circuits, SLCO-SLC7 are similar to primary link control circuits PLCO-PLC7 and function in the same manner as previously described. For eX- ample, silicon controlled rectifier STO of secondary link control circuit SLCO will assume its conductive state in response to marking potentials due to the application of positive battery marking potential from control conductor SLGC through resistor SRO and signaling conductor SLGS to the gate terminal of rectifier STO. Application of link control ground potential to signaling conductor SLOS inhibits rectifier STO from becoming conductive, thereby providing an effective open circuit in control conductor SLGC.

It may be noted at this point that, although a silicon controlled rectifier has been described for advantageous use in the link control circuits PLCG-PLC7 and SLCO- SLC7, other types of controlled rectifiers and gate circuits may be used to perform the same functions. The

9 design of such control circuits is well `within the ability of one skilled in the art.

As previously described, the criterion of coincident current flow through the differential windings of a particular ferreed crosspoint device is satisfied `by means of a common bus which interconnects the control conductors of all inputs and outputs ofthe particular array. Primary arrays PAO-PA7 and tertiary arraysTAO-TA7 have continuous common buses, PAOB-PA7B and TAOB-TA7B respectively. Secondary arrays SAO-SA7 include link selection circuits LS-LS7 in series with their associated common buses SAflB-SAB. The function of the link selection circuits LSO-LS7 is to sequentially test the electrical continuity of the primary and secondary links of which the eight possible paths between a selected line and aselectedftrunk are comprised, and to select one of the available paths for use. A more complete description of the scanning operation of the link selection circuits LSO-LS7 is included hereinbelow.

Link selection The establishment of a communications connection through'the network will now be described with reference to FIGS. 4, 5, and 6. It is assumed that a connection is desired between line L0V and trunk T0. Marking ground potential is applied by line selector 201 to control conductor LOC which is associated with line L0. Marking positive battery potential is applied through link selector control 302, conductor LSC1 and trunk selector 301 to control conductor TOC which is associated with trunk T0. It is assumed that the eight possible paths through the network between line L0 and trunk T0 are idle. As previously described, each of the eight possible paths is unique to one of the secondary arrays SAO-SA7.

One of the eight possible paths between line L0 and trunk T0 is defined by ferreed crosspoint 401 in primary array PAO, ferreed crosspoint 501 in secondary array SAO and ferreed crosspoint 601 in tertiary array TAO. Each `of the other seven paths is similarly defined by a ferreed crosspoint in primary array PAO, a ferreed crosspointy in one of' the secondary arrays SA1-SA7 and a ferreed crosspoint in tertiary array TAO.

The path defined by crosspoints 401, 501, and 601 may be traced from line selector 201 through control conductor LOC, ferreed crosspoint-101 and other ferreed crosspoints in the same horizontal coordinate of primary array PAO, common bus PAOB of primary array PAO, ferreed crosspoint 401 and other ferreed crosspoints in the same vertical coordinate of primary array PAO, control conductor PLOC including controlled rectifier PTO, ferreed crosspoint 501 and other ferreed crosspoints in the same horizontal coordinate of secondary array SAO, common bus SAOB including resistors LSRO and R0 in link selection circuit LSO, ferreed crosspoint 501 and other ferreed crosspoints in the same vertical coordinate of secondary array SAO, control conductor SLOC including controlled rectifier STO, ferreed crosspoint 601 and other ferreed crosspoints in the same horizontal coordinate of tertiary array TAO, common bus TAOB, ferreed crosspoint 601 and other ferreed crosspoints in the same vertical coordinate of tertiary array TAO and control conductor TOC to trunk selector 301. Each of the other seven paths through the network may be similarly traced.

The above-described application of marking ground and positive battery potentials to control conductors LOC and TOC, respectively, causes `controlled rectiers PTO andV STO to assume a conductive state, thereby allowing current to flow in the previously traced path defined by crosspoints 4017 501, and 601. Since all possible paths between line L0 and trunk T0 Were assumed to be idle, the controlled rectifiers PT1-PT7 and ST1-ST7, in each of the other paths similarly assume a conductive state responsive to the marking potentials applied to control conductors LOC and TOC. Had one of the possible eight paths been busy, ground control potential applied from the trunk circuit involved in the busy connection would have inhibited the rectifiers of the busy path from assuming a conductive state, thereby inhibiting current flow in the associated control conductors. The current iiow produced in the control conductors of the path LOC, SLOC, PLOC, and TOC by the application of marking potentials to control conductors LOC and T0() is of insutiicient magnitude to cause ferreed crosspoints 401, 501, and 601 and the crosspoints defining the other possible paths to assume an enabled state.

Each of the link selection circuits LSO-LS7 comprises a resistance-capacitance network having a time-constant differing from the time-contants of the resistance-capacitance networks of the other link selection circuits. These resistance-capacitance networks are arranged in such a manner that the time-constants are of increasing magnitude, with the time-constant of link selection circuit LSO as the shortest in duration and the time-constant of link selection circuit LS7 as the longest in duration. Current liow in the above-described paths between line L0 and trunk-Ttl'causes each of the eight capacitors (D0-C7 to charge through resistances Ril-R7, respectively. Due to the shorter time-constant of the resistance-capacitance network comprised of resistor R0 and capacitor C0, capacitor C0 will become fully charged before capacitors C1-C7.

Each of the link selection circuits LSG-LS? further comprises a controllable rectifier TRO-TR7, the anode and cathode elements of which are connected in series with the associated common bus SAOB-SA7B, and the gate element of which is connected through a Zener diode Ztl-Z7 to the midpoint of the respective resistance-capacitance networks. Since capacitor C0 is the first of capacitors Cil-C7 to become fully charged, the Zener diode Z0 will be `first of Zener diodes Ztl-Z7 to reach its threshold and become conductive. Zener diode Z0, in becoming conductive, allows current to fiow through the gate element of rectifier TRO. The marking ground and positive battery potentials applied to control conductors LOC and TOC are present upon the cathode and anode elements of rectifier TRO. When current is permitted to flow through the gate element of rectifier TRO by Zener diode Z0, rectifier TRO assumes a conductive state responsive to the marking potentials applied to its anode and cathode elements. The resistance offered by rectifier TRO in its conductive state is considerably less than that offered by the resistance-capacitance network comprised of resistor R0, capacitor C0 and resistance LSRO. There is, therefore, a substantial increase in current iiow through the path defined by ferreed crosspoints 401, S01, and 601 when rectifier TRO becomes conductive. This increase in current fiow is detected by link selector control 302 which then applies ground potential to conductor LSC2. Conductor LSC2 is connected in multiple to the midpoints of the resistance-capacitance networks of each link selection circuit LSO-LS7. A diode Dfi-D7 is included in series with each leg of conductor LSCZ. The application of ground to conductor LSCZ stops the charging of the capacitors C1-C7 of the other link selectioncircuits LS1- LS7, thereby halting sequential testing of the possible paths between line L0 and trunk T0.

The above-mentioned application of ground to conductor LSCZ also serves as a signal over conductor PSCI to pulse source 303. Responsive to this signal, pulse source 303 generates a high positive voltage crosspoint enabling signal and applies the crosspoint enabling signal to conductor F01, The crosspoint enabling signal is extended through the path defined by crosspoints 401, 501, and 601 and through line selector 201 to the marking ground potential applied by line selector 201. The current flow produced by the crosspoint enabling signal in this path causes ferreed crosspoints 401, 501, and 601 to assume an enabled state. As previously described, contacts 402, 502, and 602 close when their associated ferreeds 401, 501, and 601 assume an enabled state and interconnect l l signaling conductors L08, PL08, SL08, and T08, all of which are associated with the path defined by crosspoints 401, 501, and 601.

The possibility of causing an undesired ferreed crosspoint device to falsely assume an enabled state responsive to the crosspoint enabling signal is eliminated by the unidirectional current characteristics of the link control circuit rectifiers, such as rectifiers PTO-PT7 and STO-8T'7. Circuits other than the desired eight paths between line L and trunk T0 in which current fiow could be produced responsive to a coincident application of marking ground potential to control conductor LOC and of a crosspoint enabling signal to control conductor TOC are called sneak paths. All the possible sneak paths through the network necessarily extend from one switching stage to a subsequent switching stage and return to the original switching stage before completing a circuit through the network. One example of a sneak path7 referring to FIGS. 1, 2, and 3, exists from control conductor TOC through tertiary array TAO, secondary link 8L7 including link control circuit 8LC7, secondary array 8A7, secondary link SL63 including link control circuit 8LC63, tertiary array TA7, secondary link SL56 including link control circuit SLC56, secondary array SAO, primary link PLO including link control circuit PLCO and primary array PAO to control conductor LOC. The controlled rectifiers in link control circuits SLC7, SLC56, SLC63, and PLCO permit current flow through their associated control conductors in one direction only. The rectifier in link control circuit 8LC63 will not permit current to flow in a reverse direction through the control conductor 8L63C of secondary link SL63 from secondary array 8A7 to tertiary array TA7. Therefore, no current will iiow through the above traced sneak path and false enablement of crosspoint devices other than those defining the selected path is prevented.

Busy-idle switch T80 in trunk T0 has assumed its operated or busy condition since trunk T0 is engaged and is unavailable for inclusion in other connections. As previously described, link control ground potential is applied by busy-idle switch T80 to signaling conductor T08. This control ground potential is extended through contact 602, signaling conductor SL08, contact S02, signaling conductor PL08, contact 402 and signaling conductor L08. Control ground potential is thereby applied through resistors 8GRO and PGRO to the gate elements of controlled rectifiers STO and PTO, respectively. This application of ground potential to the gate elements of the controlled rectiers STO and PTO inhibits them from assuming a conductive state in response to any subsequent application of marking potentials to their respective anodes and cathodes as previously described. v

Upon the above-described establishment of the connection between trunk T0 and line L0, the marking potentials applied to control conductors LOC and TOC are removed by line selector 201 and trunk selector 301, respectively.

Transmission conductors LOR and LOT are extended through the network by contacts 403 and 404, 503 and 504, and 603 and 604, respectively, to transmission conductors TOT and TOR associated with trunk T0. The transmisison and signaling connection between line L0 and trunk T0 is maintained until crosspoints 401, 501, and 601 assume a disabled state.

It is now assumed that another connection is desired between line L23 and trunk T7. The possible paths between line L23 and trunk T7 are similar to the previously described possible paths between line L0 and trunk T0 in that they include primary links PLO-PL7 and secondary lines SLOL7. However, the paths between line L23 and trunk T7 are defined by different crosspoints than those defining the paths between line L0 and trunk T0. One such path is defined by crosspoints 411, S01, and 611 and another such path is defined by crosspoints 421, 521, and 621.

Cil

Marking ground potential is applied by line selector 201 to control conductor L23C associated with line L23. Marking positive battery potential is applied through trunk selector 301 to control conductor T7C associated with trunk T7. In a manner similar to that described for the connection between line L0 and trunk T0, the controlled rectifiers ST1-ST7 of secondary links SLI- 8L7 and the controlled rectifiers PT1-PT7 of primary links PL1-PL7 assume a conductive state responsive to the application of marking potentials to control conductors L23C and T7C. However, due to the control ground potential applied by busy-idle switch T of trunk T0 through signaling conductor T08, contact 602, signaling conductor SL08, contact 502 and signaling conductor PLOS to the gate elements of controlled rectifiers STO and PTO, controlled rectifiers STO and PTO are inhibited from assuming a conductive state. Due to the inhibiting of the rectifiers PT() and STO, no current is permitted to flow through the path between line L23 and trunk T7 which is defined by crosspoints 411, 501, and 611. In the absence of current ow through this path, capacitor C0 in link selection circuit L80 does not charge, and controlled rectitier TRO cannot assume a conductive state. Primary link PLO and secondary link SLO are therefore excluded from selection for inclusion in a connection between line L23 and trunk T7.

In a manner similar to the selection of a path between line L0 and trunk T0, the link selection circuits LS1- LS7 select a path between line L23 and trunk T7. The rst of capacitors C1-C7 to become fully charged causes the associated Zener diode Z1-Z7 to conduct, thereby producing current ow in the gate element of the associated controlled rectifier TR1-TR7 and producing an increase in current through the control conductors included in the path. The increased current is detected by link selector control 302; a ground potential is applied to conductor L8C2 to stop all other capacitors from charging; pulse source 303 is signaled to generate a crosspoint enabling signal; and the crosspoints defining the selected path assume a conductive state in response to the application of the crosspoint enabling signal to control conductor T7C.

Dz'sconnectz'on When the transfer of information over the transmission conductors of the connection between line L0 and trunk T0 is completed, busy-idle switch T80 in trunk T0 is returned to its idle position, thereby removing the control ground potential from signaling conductor T08. The removal of ground potential from signaling conductor T08 also removes ground potential from signaling conductors SL08 and PLOS of secondary link SLO and primary link PLO, respectively. The resulting removal of ground potential from the gate elements of controlled rectifiers STO and 1PT0 places them back in their noninhibited condition, wherein an application of marking potentials to their respective anode and cathode elements will cause them to assume a conductive state.

It is now assumed for illustrative purposes that busyidle switch T80 was returned to its idle position before the abovedescribed connection between line L23 and trunk T7 was established. As preivously described, marking ground potential is applied through line selector 201 to control'conductor L23C and marking positive battery potential is applied through trunk selector 301 to control conductor T7C. Since the control ground potential has.

now been removed from the signaling conductors SL08 and PL08, controlled rectifiers STO and PTO will assume a conductive state in response to the application of the marking potentials to control conductors T7C and L23C. T-he path between line L23 and trunk T7 defined by crosspoints 611, 501, and411 is now available. Since this path includes link select circuit L80whose resistancecapacitance network hasy the shortest time-constant, it will now be the path selected'for connecting line L23 to trunk T7. Upon the selection of this path, as previously described, a crosspoint enabling signal is generated by pulse source 303 and applied through link select control 302 and trunk selector 301 to control conductor T7C. The crosspoint enabling signal is extended through control conductor T7C, ferreed crosspoint 611 and other ferreed Crosspoints in the same vertical coordinate, common bus TAOB, ferreed Crosspoints `611r and 601 and other crosspoints in the same horizontal coordinate, lcontrol conductor SLOC including controlled rectifier STO, ferreed crosspoint 501, common bus SAOB including controlled rectifier TRO, ferreed crosspoint v501 and other ferreed Crosspoints in the same horizontal coordinate, control conductor PLOC including rectifier PTO, ferreed crosspoints 401 and 411 and other Crosspoints in the same vertical coordinate, common bus PAOB, ferreed crosspoint 411 and other Crosspoints in the same horizontal coordinate, control conductor L23C and line selector 201 to the applied marking ground potential. Ferreed Crosspoints 411 and 611 assume an enabled state responsive to the application of the crosspoint enabling signal. Crosspoint 501 is already in an enabled state and therefore remains in that state.

As described in the aforementioned Hayward application, a differentially wound ferreed in its enabled state will return to a disabled state responsive to a pulse applied through the ferrced device in only one coordinate direction. Crosspoints 401 and 601 were in an enabled state when the crosspoint enabling signal was applied. As described above, the path of the crosspoint enabling signal passes through Crosspoints 401 and 601 in only a single coordinate direction. Crosspoints 401 and 601 therefore assume a disabled state in response to the application of the crosspoint enabling signal, and the contacts 402, 403, and 404 and 602, 603, and 604 are opened. The connection between line L and trunk T0 is therefore broken in response to the same crosspoint enabling pulse which Was applied to establish the connection between line L23 and trunk T7.

Control circuits An illustrative circuit arrangement suitable for controlling the establishment of connections through the network is shown in FIG. 7. Its operation will be briefly described with reference to the above description of the establishment of connections through the network.

Marking positive battery potential is provided by source MVP and is applied through resistor CRI, diode CD1, the emitter element of transistor TT1 and the base element of transistor TTI to conductor LSCI. Capacitor CC1 is provided to prevent undesirable current surges through transistor TTI. Trunk selector 301 applies the marking positive battery potential present on conductor LSCl to a selected one of control conductors TOC-T63C.

As previously described, a marking ground potential is applied by line selector circuit 201 to a selected control conductor LOC-L191C and current fiows in the control conductors through the network. Selection of one of the eight possible paths through the network is made as previously described, and the current ilow in the control conductors of the selected path is increased when the appropriate rectifier TRO-TR7 assumes a conductive state. Transistor TTI is responsive to the increase in current ow through its base element to produce current fiow through its emitter element, resistor CRZ, the base element of transistor TT2 and the emitter element of transistor TT2 to ground. The current flow through the base element of transistor TT2 is sufficient t-o produce current flow between the emitter and collector elements of transistor TT2. A circuit is therefore completed rfrom ground through transistor TT2 and conductor LSC2, over which circuit the control ground potential is applied to the midpoint of the resistance-capacitance networks in link selection circuits LSO-LS7, thereby halting the above-described scanning of possible paths through the network.

Ground potential is also applied through transistor TT2 to conductor PSC1 and through the winding of relay HV to positive battery. High voltage relay HV operates over this circuit. High voltage source HVP is normally connected through resistance HVR, a break contact of relay HV and capacitor HVC to ground, thereby producing a high voltage charge in capacitor HVC. When relay HV operates as described, the high voltage charge on capacitor HVC is applied through a make contact of relay HV to conductor F01 an-d through transistor TTI, conductor LSCI and trunk selector circuit 301 to the selected control conductor TOC-T63C. The high voltage charge on capacitor HVC, when applied as described to the selected control conductor TOC-T63C, is the crosspoint enabling signal which is sufficient to operate the ferreed crosspoints defining a selected path through the network.

When trunk selector 301 and line selector 201 remove the marking potentials from the selected control conductors TOC-T63C and LOC-L191C respectively, the transistors TT1 and TT2 in link select control 302 return to their normal nonconducting state and the relay HV releases. The release of relay HV causes high voltage potential from source HVP to be again connected through capacitor HVC to ground, thereby preparing pulse source 303 to generate another crosspoint enabling signal when required.

It is to be understood that the above-described arrangements are merely illustrative of the application of the principles of the invention. Numerous other arrangements utilizing other crosspoint devices and scanning and control circuitry may be devised by those skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

1. A switching network comprising an input terminal, an output terminal; a path between said input terminal and said output terminal; a plurality of crosspoint devices defining said path; each of said crosspoint devices comprising crosspoint enabling means and connecting means; a first signaling conductor associated with said output terminal; second signaling conductors associated with said path; said connecting means controlled by said crosspoint enabling means to interconnect said first signaling conductor and said second signaling conductors; said path comprising a control conductor having said crosspoint enabling means in series therewith, and controllable rectifiers interposed between said crosspoint enabling means, each of said rectifiers having its anode and cathode elements connected in series with said control conductor and its gate element connected to one of said second signaling conductors.

2. A switching network in accordance with claim 1 wherein each of said crosspoint devices comprises a differentially wound ferreed.

3. A switching network comprising an input terminal; an output terminal; marking means for applying marking potentials to said input terminal and to said output terminal; a plurality of paths between said input terminal and said output terminal defined by crosspoint devices; idle path selecting means comprising said plurality of paths, scanning means for sequentially determining from each of said plurality of paths the electrical continuity thereof, detection means responsive to a determination by said scanning means that one of said plurality of paths is electrically continuous for disabling said scanning means, and pulsing means controlled by said detection means for applying a crosspoint enabling signal to said output terminal.

4. A switching network comprising an input terminal; an output terminal; a signaling conductor associated with said output terminal; marking means for applying marking potentials to said input terminal and to said output terminal; crosspoint devices denng paths between said input terminal and said output terminal, each of said crosspoint devices comprising crosspoint enabling means and connecting means; idle path selection means including said paths and responsive to said marking means for selecting an idle one of said paths; pulsing means controlled by said idle path selection means for enabling said crosspoint enabling means of those of said crosspoint devices which define said selected idle path; said connecting means responsive to said crosspoint enabling means for extending said signal conductor through said network in association with said selected path; means for applying a control potential to said signaling conductor; and control means associated wtih said selected path and responsive to said control potential to exclude said selected path from said idle path selection means,

S. A switching network comprising an input terminal having a first signaling conductor associated therewith; an output terminal having a second signaling conductor associated therewith; marking means for applying marking potentials to said input terminal and to said output terminal; crosspoint devices defining paths between said input terminal and said output terminal; selection means including all idle ones of said paths and responsive to said marking means for selecting an idle one of said paths; each of said crosspoint devices comprising crosspoint enabling means and connecting means; pulsing means controlled by said selection means for enabling said crosspoint enabling means of those of said crosspoint devices which define said selected idle one of said paths, said connecting means responsive to said crosspoint enabling means to interconnect said first signaling conductor and said second signaling conductor; means for applying control potential to said second signaling conductor; and control means associated with said connecting means and responsive to said application of control potential to said second signaling conductor to exclude said selected idle one of said paths from said selection means.

6. A switching network comprising an input terminal; an output terminal; paths between said input terminal and said output terminal; crosspoint devices defining said paths, each of said paths comprising links interconnectable by said crosspoint devices; each of said links comprising a control conductor, a signaling conductor and a controllable rectifier having its anode and cathode elements connected in series with said control conductor and its gate element connected to said signaling conductor; each of said crosspoint devices comprising crosspoint enabling means connected in series with the control conductors of the particular links which are interconnectable by a crosspoint device and connecting means responsive to said crosspoint enabling means to interconnect the signaling conductors of said particular links; said rectifier responsive to marking potentials applied to the distal ends of said control conductor to produce current ow through said control conductor and controlled by a continuous control potential applied to said signaling conductor to inhibit current fiow responsive to subsequently applied marking potentials.

7. A switching network comprising an input terminal; an output terminal; paths between said input terminal and said output terminal; a first signaling conductor associated with said output terminal; second signaling conductors individually associated with each of said paths; crosspoint devices each of which defines one of said paths and which comprises crosspoint enabling means connected in series with .said defined path and connecting means responsive to said enabling means for connecting said first signaling. c-onductor to the one of said second signaling conductors associated with said defined path; marking means for .applying Imarking potentials to said input terminal and to said .output terminal; idle path selecting means responsive to said marking means and comprising scanning means for sequentially determining the electrical continuity of each of said paths, detection means responsive to a determination by said scanning means that one of said paths is electrically continuous for disabling said scanning means, and pulsing means controlled by said detection means for applying a crosspoint enabling signal to said output terminal; and switching means individually associated with each of said paths and responsive to a continuous control potential applied to said first signaling conductor to effect an open circuit in said defined path.

8. A switching network comprising an input terminal; an output terminal; a path between said input terminal and said output terminal defined by a first crosspoint device in a first switching stage, a second crosspoint device in an intermediate switching stage and a last crosspoint device in a last switching stage; each of said crosspoint devices comprising crosspoint enabling means and connecting means; said path comprising a control conductor having said enabling means of said first, second, and last crosspoint devices in series therewith; a first link comprising a first segment of said control conductor defined by said first and second crosspoint devices, a first signaling conductor and a tirst controllable rectiiier having its anode and cathode elements in series with said first segment of said control conductor and its gate element connected to said first signaling conductor; a second link comprising a second segment of said control conductor defined by said second and last crosspoint devices, a second signaling conductor and a second controllable rectifier having its anode and cathode elements in series with said second segment of said control conductor and its gate element connected to said second signaling conductor; said first and second rectiiers conductive in response to marking potentials applied to said input terminal and to said output terminal; said crosspoint enabling means enabled by a crosspoint enabling signal applied to said -output terminal coincident with a marking potential applied to said input terminal when said rectifiers are conductive; a third signaling conductor associated with said output terminal; said connecting means responsive to said enabled crosspoint enabling means to interconnect said first, second, and third signaling conductors; said rectifiers controlled by a continuous control potential applied to said third signaling conductor to inhibit conduction through said first and second rectifiers in response to subsequent applications of marking potentials and crosspoint enabling signals to said terminals.

9. In a switching network a crosspoint device comprising crosspoint enabling means and connecting means; and control means for controlling said crosspoint device cornprising a control conductor having said crosspoint enabling means in series therewith, a first signaling conductor and a second signaling conductor both of which are associated with said crosspoint device, said connecting means responsive to said enabling means for connecting said first signaling conductor to said second signaling conductor, and switching means connected in series with said control conductor and responsive to marking potentials applied thereto to produce current fiow through said control conductor and responsive to a control potential applied through said first signaling conductor and said connecting meansto said second signaling conductor to inhibit current fiow through said control conductor.

10. In a switching network the combination described in claim 9 wherein said crosspoint device comprises a differentially wound ferreed.

11. In a switching network a crosspoint device cornprising crosspoint enabling means and connecting means controlled by said crosspoint enabling means; means for controlling said -crosspoint device comprising a control conductor having said crosspoint enabling means in series therewith for applying crosspoint enabling signals and for extending marking potentials applied thereto through said network, a first signaling conductor and a second signaling conductor both of which are associated with said crosspoint device, said connecting means responsive to said crosspoint enabling means to connect said first signaling conductor to said second signaling con` ductor, and a controllable rectifier having its anode and cathode elements connected in series with said control conductor and its gate element connected to said second signaling conductor; said rectifier responsive to said marking potentials applied to said control conductor to produce current flow through said control conductor and controlled by a control potential applied through said first signaling conductor and said connecting means to said second signaling conductor to inhibit current fiow through said control conductor responsive to said marking potentials.

12. In a Iswitching network a crosspoint device comprising crosspoint enabling means controllable in a first manner to assume an enabled state responsive to an application of a crosspoint enabling signal and controllable in a second manner to assume a disabled state responsive to a subsequent application of a crosspoint enabling signal; and control means for controlling said applications of said crosspoint enabling signals comprising a control conductor having said crosspoint enabling means in series therewith for applying said crosspoint enabling signals, a signaling conductor associated with said crosspoint device, and switching means connected in series with said control conductor and responsive to a control potential applied to said signaling conductor to inhibit said applications of `said crosspoint enabling signals through said crosspoint enabling means.

13. In a switching network the combination described in claim 12 wherein said crosspoint device comprises a differentially wound ferreed.

14. In a switching network a crosspoint device comprising crosspoint enabling means controllable in a first manner to assume an enabled state responsive to an application of a crosspoint enabling signal and controllable in a second manner to assume a disabled state responsive to a subsequent application of a crosspoint enabling signal and connecting means Icontrolled by said crosspoint enabling means; and control means for controlling said 'applications of said crosspoint enabling signals comprising a control conductor having said crosspoint enabling means in series therewith for applying said crosspoint enabling signals and for extending marking potentials applied thereto through said network, a first signaling conductor and a second signaling conductor both of which are associated with said crosspoint device, said connecting means responsive to said crosspoint enabling means in said enabled state to connect said first signaling conductor to said second signaling conductor, a controllable rectifier having its anode and cathode elements connected in series with said control conductor and its gate element conne-cted to said second signaling conductor, said rectifier responsive to said marking potentials to permit application of said crosspoint enabling signals through said crosspoint enabling means and controlled by a control potention applied through said first signaling conductors and said connecting means to said second signaling conductors to inhibit application of said crosspoint enabling signals through said crosspoint enabling means.

1S. A switching network comprising an array of ferreed switches each including first and second winding means and a plurality of contact means, a first common bus to which all of said ferreed switch first winding means are connected, a second common bus to which all of said ferreed switch second winding means are connected, gat- 18 ing means interconnecting said first common bus and said second common bus, said gating means including a control terminal, and charging means in parallel with said gating means and connected to the control terminal thereof.

16. A Iswitching network comprising an array of ferreed switches each including first and second winding means and a plurality of contact means, a first common bus to which all of said ferreed switch first winding means are connected, a second common bus to which all of said ferreed switch second winding means are connected, a silicon controlled rectifier gating element interconnecting said first common bus and said second common bus, said silicon -controlled rectifier having anode, cathode and gate terminals, said anode terminal of said rectifier being connected to said first common bus and said cathode terminal of said rectifier being connected to said second common bus, a charging circuit comprising a series resistor and capacitor in parallel with said silicon controlled rectifier to interconnect said first common bus and said second common bus, and a voltage threshold element connected between the junction of said series connecte-d resistor and capacitor and the gate terminal of said silicon controlled rectifier.

17. A switching network in accordance with claim 16 wherein said voltage responsive element comprises a zener diode.

18. In a switching network, a crosspoint device comprising crosspoint enabling and connecting means controlled by said crosspoint enabling means; means for controlling said crosspoint device comprising a control conductor having said crosspoint enabling means in series therewith, a signaling conductor associated with said crosspoint device, a controllable rectifier having its anode and cathode elements connected in series with said control conductor and its gate element connected to said signalling conductor, means including said control conductor for applying marking potentials to said rectifier to complete a current path through said control conductor, means for applying a crosspoint enabling signal through said marked current path to said crosspoint enabling means, and said rectifier responsive to a control potential applied to said signaling conductor to open said current path.

19. In a switching network, a crosspoint switch device -comprising a ferreed switch having a pair of windings and a plurality of contact means, means for connecting said windings in series, a signaling conductor connected to one of said contact means, a control conductor connected to one of said windings, and three-terminal rectifier means having its input and output terminals connected in series with said control conductor and its gating terminal connected to said signaling conductor.

References Cited by the Examiner UNITED STATES PATENTS ROBERT H. ROSE, Primary Examiner. 

3. A SWITCHING NETWORK COMPRISING AN INPUT TERMINAL; AN OUTPUT TERMINAL; MARKING MEANS FOR APPLYING MARKING POTENTIALS TO SAID INPUT TERMINAL AND TO SAID OUTPUT TERMINAL; A PLURALITY OF PATHS BETWEEN SAID INPUT TERMINAL AND SAID OUTPUT TERMINAL DEFINED BY CROSSPOINT DEVICES; IDLE PATH SELECTING MEANS COMPRISING SAID PLURALITY OF PATHS, SCANNING MEANS FOR SEQUENTIALLY DETERMINGING FROM EACH OF SAID PLURALITY OF PATHS THE ELECTRICAL CONTINUITY THEREOF, DETECTION MEANS RESPONSIVE TO A DETERMINATION BY SAID SCANNING MEANS THAT ONE OF SAID PLURALITY OF PATHS IS ELECTRICALLY CONTINUOUS FOR DISABLING SAID SCANNING MEANS, AND PULSING MEANS CONTROLLED BY SAID DETECTION MEANS FOR APPLYING A CROSSPOINT ENABLING EQUAL TO SAID OUTPUT TERMINAL.
 9. IN A SWITCHING NETWORK A CROSSPOINT DEVICE COMPRISING CROSSPOINT ENABLING MEANS AND CONNECTING MEANS; AND CONTROL MEANS FOR CONTROLLING SAID CROSSPOINT DEVICE COMPRISING A CONTROL CONDUCTOR HAVING SAID CROSSPOINT ENABLING MEANS IN SERIES THEREWITH, A FIRST SIGNALLING CONDUCTOR AND A SECOND SIGNALLING CONDUCTOR BOTH OF WHICH ARE ASSOCIATED WITH SAID CROSSPOINT DEVICE, SAID CONNECTING MEANS RESPONSIVE TO SAID ENABLING MEANS FOR CONNECTING SAID FIRST SIGNALLING CONDUCTOR TO SAID SECOND SIGNALING CONDUCTOR, AND SWITCHING MEANS CONNECTED IN SERIES WITH SAID CONTROL CONDUCTOR AND RESPONSIVE TO MARKING POTENTIALS APPLIED THERETO TO PRODUCE CURRENT FLOW THROUGH SAID CONTROL CONDUCTOR AND RESPONSIVE TO A CONTROL POTENTIAL APPLIED THROUGH SAID FIRST SIGNALLING CONDUCTOR AND SAID CONNECTING MEANS TO SAID SECOND SIGNALLING CONDUCTOR TO INHIBIT CURRENT FLOW THROUGH SAID CONTROL CONDUCTOR. 